An optical disc such as a compact disc (CD), a digital versatile disc (DVD), and a “Blu-ray Disc™” (BD) has been increasingly used now as large capacity storage media. Laser diodes used for reading/writing from/to these discs have respective different emission wavelengths: a CD laser diode has an emission wavelength of 780 nm band (infrared), a DVD laser diode has an emission wavelength of 650 nm band (red), and a BD laser diode has an emission wavelength of 405 nm band (blue-violet). Hence, in order to treat data for a CD, a DVD, and a BD in a single optical disc drive, required are three light sources of infrared, red, and blue-violet.
In a case of configuring a multi-wavelength semiconductor laser device such that different wavelength laser-diode chips are arranged side by side, their emission points are spaced largely apart from each other, resulting in difficulty in optical design. For dealing therewith, there has been a conventional multi-wavelength semiconductor laser device, in which red and infrared laser diodes are arranged in parallel and bonded on a blue-violet laser diode that is mounted on a heat sink, to be able to treat data for CD, DVD, and BD in a single optical disc drive (see, for example, JP 2006-59471A).
In the multi-wavelength semiconductor laser device described in JP 2006-59471A, however, since the infrared and the red laser diodes are bonded on the blue-violet laser diode, there has been a problem in that heat generated during operation of the infrared and the red laser diodes cannot efficiently dissipate to the heat sink. Moreover, this configuration makes their assembly process complicated, resulting in a problem of high manufacturing costs.